Technical Field
The present disclosure relates to a touch display device, and more particularly, to a touch display device where reduction in touch accuracy due to a transient noise is prevented by sequential and overlapping driving of a plurality of touch electrodes and a method of driving the touch display device.
Discussion of the Related Art
As an information society progresses, display devices have rapidly advanced and various flat panel displays (FPDs) have been developed. For example, the FPDs include a liquid crystal display (LCD) device, a plasma display panel (PDP) device, an organic light emitting diode (OLED) display device and a field emission display (FED) device. Since the FPDs have advantages such as a thin profile, a light weight and a low power consumption, cathode ray tube (CRT) devices have been widely substituted by the FPDs.
Recently, a touch display device where a touch panel is disposed over a display panel has been a subject of research. The touch display device is used as an output unit displaying an image and as an input unit receiving an order of a user by a touch of a specific portion of the image. The touch panel may be classified into a pressure sensing type, a capacitance type, an infrared type and an ultrasonic type according to a sensing type.
When a user watches the image displayed by the display panel and touches the touch panel, the touch panel detects a position information of the corresponding portion and recognizes an order of the user by comparing the detected position information with a position information of the image.
The touch display device may be fabricated such that an individual touch panel is attached to a display panel. Recently, for slimness of a portable terminal such as a smart phone and a tablet PC, a demand for an in-cell touch display device where a touch panel and a display panel are integrated by using an electrode or a line for the display panel as an electrode and a line for the touch panel has increased.
FIG. 1 is a plan view showing an in-cell touch display device according to the related art. Specifically, FIG. 1 shows a self-capacitance type in-cell touch display device.
In FIG. 1, a self-capacitance type in-cell touch display device 10 according to the related art includes a touch display panel 20 and a touch display driving unit 30.
The touch display panel 20 displays an image and senses a touch. For sensing a touch, the touch display panel 20 includes a plurality of touch electrodes TE11 to TE58 and a plurality of touch lines TL11 to TL58 connecting the plurality of touch electrodes TE11 to TE58 and the touch display driving unit 30. The plurality of touch electrodes TE11 to TE58 may be disposed in a matrix of 5 rows by 8 columns.
The touch display driving unit 30 senses a position of a touch. The touch display driving unit 30 applies a touch scan signal to the plurality of touch electrodes TE11 to TE58 and detects the position of the touch by analyzing a change in a capacitance of the plurality of touch electrodes TE11 to TE58 according to the touch scan signal.
The touch display driving unit 30 includes a plurality of multiplexers (MUXs) 32, an analog front end part 34, an analog-digital converting part 36 and a signal processing part 38.
An input terminal 32a of each of the plurality of MUXs 32 is connected to the plurality of touch lines TL11 to TL58, and an output terminal 32b of each of the plurality of MUXs 32 is connected to the analog front end part 34. The input terminal 32a and the output terminal 32b of the plurality of MUXs 32 are sequentially connected.
For example, the plurality of MUXs may include first to eighth MUXs, a channel ratio of the input terminal 32a and the output terminal 32b of each of the first to eighth MUXs is 5:1, and the output terminal 32b is sequentially connected to one of the five input terminals 32a. 
The input terminal 32a of the first MUX is connected to the 11th to 51st touch lines TL11 to TL51 respectively connected to the 11th to 51st touch electrodes TE11 to TE51 of the first column of the touch display panel 20, and the output terminal 32b of the first MUX is sequentially connected to the input terminals 32a of the first MUX.
As a result, the first MUX sequentially transmits the touch scan signal to the 11th to 51st touch lines TL11 to TL51 of the first column and sequentially transmits a touch sensing signal of the 11th to 51st touch lines TL11 to TL51 of the first column to the analog front end part 34.
Similarly to the first MUX, the second to eighth MUXs are connected to corresponding touch lines of 12th to 58th touch lines TL12 to TL58, respectively.
The analog front end part 34 transmits the touch sensing signal to the analog-digital converting part 36. The analog-digital converting part 36 converts the touch sensing signal of an analog type to the touch sensing signal of a digital type and transmits the touch sensing signal of the digital type to the signal processing part 38.
The signal processing part 38 calculates a touch variance from the touch sensing signal and judges a touch presence from the touch variance.
The touch display driving unit 30 calculates coordinates of a touch input from the touch variance.
The self-capacitance type in-cell touch display device 10 is driven by classifying one frame into a display period for displaying an image and a touch period for sensing a touch.
The touch display driving unit 30 classifies the touch period into a plurality of MUX periods where the plurality of MUXs 32 transmit the touch scan signal to the plurality of touch electrodes, respectively. The touch display driving unit 30 transmits the touch scan signal to one of the plurality of touch electrodes many times during each of the plurality of MUX periods and detects the touch sensing signal many times to calculate the touch variance.
TABLE 1 is a table showing a touch electrode where a touch scan signal is applied and a touch sensing signal is detected during a plurality of MUX periods of a self-capacitance type in-cell touch display device according to the related art.
TABLE 1PeriodMP1MP2MP3MP4MP5SensingTE11TE21TE31TE41TE51Electrode
In TABLE 1 and FIG. 1, the first MUX of the touch display driving unit 30 transmits a pulse of the touch scan signal to the 11th touch electrode TE11 10 times during a first MUX period MP1 of the touch period and transmits the corresponding touch sensing signal from the 11th touch electrode TE11 to the analog front end part 34 10 times. The signal processing part 38 of the touch display driving unit 30 calculates a capacitance variation of the touch variance from an average value of the touch sensing signals of 10 times.
Similarly, the first MUX of the touch display driving unit 30 transmits a pulse of the touch scan signal to the 21st to 51st touch electrodes TE21 to TE51 10 times during second to fifth MUX periods MP2 to MP5, respectively, of the touch period and transmits the corresponding touch sensing signal from the 21st to 51st touch electrodes TE21 to TE51 to the analog front end part 34 10 times. The signal processing part 38 of the touch display driving unit 30 calculates a capacitance variation of the touch variance from an average value of the touch sensing signals of 10 times.
Accordingly, the plurality of MUXs 32 of the touch display driving unit 30 transmit the touch scan signal to one of the plurality of touch electrodes TE11 to TE58 many times during the plurality of MUX periods, respectively, of the touch period and transmit the touch sensing signal from one of the plurality of touch electrodes TE11 to TE58 to the analog front end part 34 many times. The signal processing part 38 of the touch display driving unit 30 calculates the touch variance from the average value of the touch sensing signals of the many times.
When a transient noise component is inputted to the touch display device, the noise component causes an interference and a distortion of the touch sensing signal to generate an error in calculation of the touch variance.
Specifically, when the number of detection of the touch sensing signal is relatively small, the error in calculation of the touch variance increases to reduce the accuracy of touch detection.
When the number of detection of the touch sensing signal increases to prevent the reduction of accuracy, the touch period for sensing a touch increases and the display period for displaying an image decreases. As a result, a display quality of the image is deteriorated.